单项选择题
A.the solid waste dump chute
B.an access door
C.the same way for waste oil burners
D.a changing opening
单项选择题 If plastic film insulation becomes damaged in air conditioning system, （） may form within the film.
单项选择题 Under tropical conditions, control valves have fully opened, but the room still hot.What measures can be taken in such a case?（）
单项选择题 Under normal conditions, the quantity of air circulation becomes less and less.What is the reason?（）